Purification of Metals

ABSTRACT

A solid composition comprises:
         MnO 2 ; and   a compound represented by the general formula (I)       

     
       
         
         
             
             
         
       
         
         wherein: 
         R is a polymer; 
         each Y is independently a hydrogen or a negative charge; 
         Z is either hydrogen or is not present; 
         each n is independently 1, 2, 3, 4, 5 or 6; 
         wherein the MnO 2  is bound to the compound of formula (I) so as to coat the surface thereof. Such a composition may be used for the separation of polyvalent metal species, such as Mo, from one or more accompanying impurities.

This application is a continuation of U.S. patent application Ser. No.12/676,197 filed on Mar. 3, 2010, which is a National Stage Applicationof PCT/US2008/075759, filed Sep. 10, 2008, which claims the benefit ofUK Application No. GB 0717612.6 filed Sep. 10, 2007, the entiredisclosures of all these applications being incorporated herein byreference.

The present invention relates to the purification of metals. Inparticular, though not exclusively, it relates to a composition and amethod for the separation of particular polyvalent metal species fromone or more accompanying impurities.

The separation of the isotope Mo-99 from an aqueous solution containinga mixture of nuclear fission products may be used to illustrate thebackground to the present invention. Mo-99 is one of the isotopesgenerated as a result of nuclear fission processes involving uranium. Ofall of the fission products which are generated, Mo-99 is of particularinterest, since a subsequent radioactive decay product of Mo-99 is^(99m)Tc, which is used in medicine, e.g. for the diagnosis of organfailure and also for the treatment of tumours.

However, when dealing with the separation of a mixture of fissionproducts containing Mo-99, it is of importance that all of the processsteps are performed as rapidly and efficiently as possible as the Mo-99isotope decays quickly. Mo-99 decays to ^(99m)Tc with a half-life ofjust 66 hours. Furthermore, the physical decay characteristics of Mo-99are such that only 88.6% of the decaying Mo-99 atoms form ^(99m)Tc. Thismeans that only 78% of the activity remains after 24 hours; 60% remainsafter 48 hours, and so on. Therefore, the yield of Mo-99 obtained isdependent upon the speed of the separation process as well as itsefficiency, as the longer the process takes, the less remaining Mo-99there will be to recover. Because of this, any improvement in theprocess, however seemingly slight, which can be easily incorporated intothe existing separation process or which can replace existing processsteps is, therefore, of great commercial interest.

The process currently used for the separation of Mo-99 from otherfission products is described in U.S. Pat. No. 5,508,010 and Sameh(Production of Fission Mo-99 from LEU Uranium Silicide Target Materials,Invited Papers on 2000 Symposium on Isotope and Radiation Applications,May 18-20 2000, Institute of Nuclear Energy Research, Taiwan). Itinvolves bringing an aqueous solution of the mixture containing Mo-99and the other fission products into contact with a packed bed ofmanganese dioxide (MnO₂). The Mo-99 (in the form of [⁹⁹MoO₂]²⁺) isretained by the MnO₂ bed by means of adsorption, together with some ofthe other fission products, while the remainder of the unwanted fissionproducts, together with any anionic species, are removed along with theaqueous solution.

The MnO₂ used in the packed bed in U.S. Pat. No. 5,508,010 has aparticle size of 0.2-0.5 mm from which any finer particles have beenpreviously removed by liquid sedimentation. This is because particlessmaller than 0.2 mm are said to be able to be washed out of the columntogether with the unwanted fission products, while carrying some of thetarget Mo-99. This loss of Mo-99 attached to the small MnO₂ particlesdecreases the final yield of Mo-99.

The mixture of fission products containing the Mo-99 is added to theMnO₂ packed bed in a solution of 3M nitric acid, or 2M sodium nitrateand 1M nitric acid. After the mixture is completely added, the column iswashed with more nitric acid and water.

The MnO₂ packed bed containing the adsorbed Mo-99 is dissolved in a 2Msulphuric acid solution containing SCN⁻, SO₃ ²⁻ and I⁻ ions. Theresultant solution is then run through a column of Chelex® 100 (which isa chelate-forming ion-exchanger based on a styrene-divinylbenzenecopolymer having iminodiacetate groups) which has been pre-conditionedby a sulphuric acid solution containing the same ions. The chargedcolumn is then washed, in sequence, with 2M sulphuric acid containingrhodanide (i.e. thiocyanate) and sulfite ions, and then with water.Under these conditions, a molybdenum complex, [Mo-99(SCN)₆]³⁻, isformed. This complex is selectively bound by the Chelex, removing itfrom the solution of unwanted components, and helping to remove most ofany remaining impurities in the Mo-99. The final Mo-99 separation (i.e.to effect its removal from the Chelex) is performed with 1M caustic sodasolution heated to 50° C. This final basifying step changes the chargeon the Chelex from positive to negative, thus changing it to a cation,rather than anion, exchanger. The Mo-containing anions are thus elutedas [MoO₄]²⁻, the normal form of Mo in basic solutions. A similarseparation/purification approach may be employed for other polyvalentmetal ions, particularly transition metal ions, exhibiting the abilityto form anionic complexes in acidic solution.

Importantly, the Chelex must not come into contact with nitrates, hencethe need for the MnO₂ packed bed, containing the Mo-99, to be washed ofnitric acid prior to dissolution in sulphuric acid solution.

As mentioned above, any improvement in the design of the process whichcan bring about a greater efficiency in terms of speed of separation oryield is of significant commercial interest.

Therefore, in accordance with the present invention, there is provided asolid composition comprising:

MnO₂; and

a compound represented by the general formula (I)

wherein:R is a polymer;each Y is independently a hydrogen or is not present;Z is either hydrogen or is not present;each n is independently 1, 2, 3, 4, 5 or 6;wherein the MnO₂ is bound to the compound of formula (I) so as to coatthe surface thereof.

The composition of the invention allows nitrate-rich (from nitric acid)eluates from Mo-99 generators, or other isotope production processes, tobe loaded directly into a vessel containing the composition. The MnO₂coating effectively shields the compound of formula I from the nitrates.The Mo-99, or other desired metal, can thus be adsorbed onto the MnO₂,and the nitrate solution washed away. The subsequent exposure of thecompound of formula I (as described in more detail below), allows thefurther purification of the Mo-99, or other desired metal, in the samevessel. The ability to perform the separation/purification in a‘one-shot/one-pot’ manner leads to improvements in efficiency and/oryield for all polyvalent metal ions amenable to separation using theMnO₂/Chelex approach, regardless of whether the input materialcontaining the desired metal is rich in nitrates or not.

In certain embodiments of the invention, the coating of the compounds offormula I with MnO₂ is substantially complete. It is preferred that atleast 50% of the surface of the compounds of formula I is coated withMnO₂, more preferably at least 60%, even more preferably at least 75%,most preferably at least 90%.

Although R may be a homopolymer, it is preferably a copolymer. Preferredpolymers for use in compositions of the invention are hydrophobicpolymers, in some instances containing aromatic groups (such as phenylgroups) within their structure. Included amongst the monomers which mayform the homopolymer or part of the copolymer R are styrene,divinylbenzene, and derivatives thereof. In certain embodiments, R is acopolymer of styrene and divinylbenzene. Preferably, R is a crosslinkedpolystyrene, which may be formed by the addition of a quantity (forexample, 0.5-25%) of a crosslinking agent, such as divinylbenzene, tostyrene during polymerisation.

While the variable n may in each instance independently represent anyinteger from 1-6, n may be the same integer (1, 2, 3, 4, 5 or 6) in eachcase, and is preferably 1 in each case.

It is the COOY groups in the compound of formula (I) which are importantin the chelation of polyvalent metal ions, such as Mo-99. The mostpreferred compounds of formula (I) are Chelex® 100 or Chelex® 20 (mostpreferably Chelex® 100), which are styrene-divinylbenzene copolymersbearing iminodiacetate groups. Such compounds exhibit levels ofselectivity for divalent metal ions over monovalent metal ions of about5,000 to 1, and the levels of selectivity remain high even in highlyconcentrated salt solution.

Chelating resins such as Chelex® 100 or Chelex® 20 are available asAnalytical Grade Chelex 100 resin, Biotechnology Grade Chelex 100 resin,and Technical Grade Chelex 20 resin. Biotechnology Grade Chelex 100resin is analytical grade resin which is certified to contain less than100 micro-organisms per gram of resin. Technical Grade Chelex 20 resinis a coarse mesh resin. In principle both Chelex 20 and Chelex 100 canbe used in compositions of the invention. Chelex 20 has a lower degreeof purification, however, and has a larger particle size (20-50 mesh,i.e. around 0.85-0.3 mm) and is hence less preferred. It is potentiallymore advantageous to use Chelex 100 of particle size 100-200 mesh(approximately 0.15-0.075 mm) or 200-400 mesh (approximately 0.075-0.037mm) in compositions of the present invention.

Chelex resins are classed with the weakly acidic cation exchange resinsdue to the presence of the carboxylic acid groups, but they differ fromordinary exchangers because of the high selectivity for metal ions andmuch greater bond strength. They operate mostly in basic, neutral, andweakly acidic solutions of pH 4 or higher. At very low pH, the resinacts as an anion exchanger. The structure of the Chelex varies with pH.For example, at a pH of about 2, Y═H and Z═H (i.e. the nitrogen atom ispositively charged). At more weakly acidic pHs, such as 4, one of theCOOY groups of the iminodiacetate groups is deprotonated to form azwitterionic structure. At a neutral pH, both the COOY groups of theiminodiacetate groups are deprotonated, and at a basic pH, the nitrogenatom is also deprotonated.

The composition of the invention can act both as a cationic exchanger(both when the MnO₂ is present and also subsequent to removal of theMnO₂ and once the pH is raised (due to the COO⁻ groups of the compoundof formula (I) thereby formed)), and also as an anionic exchanger (dueto the compound of formula (I)), following the dissolution of the MnO₂in an acidic medium. It can therefore also be used in other applicationswhere the desired metal species can shift from cationic to anionicspecies in acidic media. The composition of the invention can be used tobind any cationic species from solution. It has an additional advantage,however, of being able to separate different cations upon chemicaltransformation of one of the cationic species in acid media (i.e. analteration in complexation or oxidation state) because the transformedspecies can then be captured by an anionic exchanger (i.e. the compoundof formula I, such as Chelex, which remains). Additionally, compounds offormula I, such as Chelex, are able to function as cationic exchangersthemselves in basic media. This allows for release of the anionictransformed species by addition of base.

Although MnO₂ exists in a lattice structure, the MnO₂ has OH groups onits surface, the ‘free’ oxygen atoms at the surface which are only boundto one manganese atom being terminated by protons. The compound offormula (I) is able to bind to the MnO₂ due to the presence of thesesurface OH groups. The manner in which this occurs is dependent upon theprecise synthetic process undertaken to prepare the composition.However, since the compound of formula I can bind to cations or anionsdepending on the pH of the surrounding media, the synthetic process canbe relatively flexible.

The composition of the invention is preferably in particulate form.

The composition of the invention is intended to be used in theseparation of polyvalent metal ions from accompanying impurities, suchas the separation of Mo-99 from other fission products, in place of thepure MnO₂ particles which are used in the column (i.e. the packed bed)for the adsorption of Mo-99 as in U.S. Pat. No. 5,508,010. Thecomposition of the invention is preferably presented in a column havingone or more closable inlets and outlets.

The composition of the invention has the advantage that it allows thecollection, in a ‘one-pot, one-shot’ manner, of substantially all thedesired polyvalent metal ion, such as Mo-99, retained by the MnO₂following the latter's dissolution. This improves the process time(which, in the case of the separation of radioactive isotopes, in turnincreases the final yield of desired fission products) and reduceslosses in the process due to transferring materials from one separationmedium to another.

Also provided, in another aspect of the invention, is a method ofseparating a desired polyvalent metal species from one or moreaccompanying impurities, the method comprising:

(i) contacting the desired polyvalent metal species and accompanyingimpurities with a composition of the invention as described above andallowing the desired polyvalent metal species to bind to thecomposition;(ii) dissolving the MnO₂ and the desired polyvalent metal species boundthereto to form a solution thereof; and(iii) contacting the solution with a complexing agent and enabling thesolution to come into contact with the compound of formula I exposed asa result of the dissolution of step (ii).

In step (ii), the MnO₂ (and bound desired polyvalent metal species) ispreferably dissolved in sulphuric acid, such as 2M sulphuric acid.

The desired polyvalent metal species is any such species which displaysthe ability to selectively form anionic complexes with anionic ligandsin acidic solution. The desired polyvalent metal species may beradioactive or non-radioactive. Such species include Mn, Co, Ni and Pt(which form [M^(II)(SCN)₄]²⁻ species upon reduction and treatment withSCN ions), Fe, Co and Mo (which form [M^(III)(SCN)₆]³⁻ species uponreduction and treatment with SCN ions or, in the case of Co, upontreatment with SCN ions without the reduction step), Sn and Pb (whichform [M^(IV)(SCN)₆]²⁻ species upon treatment with SCN ions), and Fe(which forms [M^(II)(SCN)₆]⁴⁻ species upon reduction and treatment withSCN ions). In one possible application of the composition of theinvention, it may be used as part of an analysis of Pb-containingsolutions.

The desired polyvalent metal species is preferably a transition metal,such as Mn, Co, Ni, Pt, Fe or Mo. The desired polyvalent metal speciesis, in certain embodiments, a radioactive isotope. In exemplaryembodiments, the desired polyvalent metal species is an isotope of Mo.In particular embodiments, the desired polyvalent metal species isMo-99, the accompanying impurities including other fission products,e.g. from a generator eluate.

The complexing agent used in step (iii) may be any suitable mono- ormultidentate ligand. In certain embodiments, the complexing agentcomprises a monodentate ligand, such as rhodanide (i.e. thiocyanate)ions. The complex of Mo-99 with rhodanide is coloured, hence providing arobust test for identifying, at least qualitatively, the presence ofMo-99.

The method of the present invention may, in certain embodiments, includethe addition of a reducing agent in step (iii). Mo, Mn, Pt, Co, Fe andNi may be purified via complexation with SCN ions when reduced to the +2(Mn, Co, Ni, Fe and Pt) or +3 (Mo and Fe) oxidation states. Complexationmay, however, take place without a reduction step in the case ofCo^(III), Pb^(IV) and Sn^(IV) complexes. Accordingly, it may beappropriate to reduce the oxidation state of the desired metal speciesas part of step (iii). The reducing agent in step (iii) may be selectedfrom the group consisting of iodide ions, sulphite ions, metallic zinc,metallic aluminium, and combinations thereof. In particular, acombination of iodide and sulphite ions may be used.

If a reducing agent is not required as part of step (iii), the desiredpolyvalent metal species may be purified by the method of the inventionin the higher oxidation state suitable for complex formation.

The method of the invention is preferably carried out in one or morecolumns packed with the composition of the invention. The method mayalso employ one or more columns packed with compound of formula I forbinding complexed desired polyvalent metal species, such as Mo-99,following steps (i)-(iii). Such an arrangement may increase the overallcapacity of the method and increase the overall efficiency of desiredpolyvalent metal species recovery. Thus, in an embodiment, a firstcolumn is used which contains particles of the composition of theinvention. The first column is connected to a second column such thatthe eluate from the first column enters the second column, the secondcolumn containing particles of compound of formula I. The particles inthe first column may have a size of around 100-200 mesh, whilst thesecond column may contain particles of around 200-400 mesh.

The invention also provides the use of a composition of the invention asdescribed above, in the separation of a desired polyvalent metal speciesfrom one or more accompanying impurities.

In particular embodiments, the composition of the invention is used forthe separation of Mo-99 from a mixture of fission products.

The process of the invention, as used for the separation of Mo-99 fromthe other fission products (for the purposes of illustration) is, inoverall terms, similar to that described in U.S. Pat. No. 5,508,010. Itcomprises bringing an aqueous solution of the mixture containing Mo-99and the other fission products into contact with a packed bed comprisingthe composition of the invention. The Mo-99 (in the form of[Mo-99O₂]²⁺), together with some of the other fission products, isretained by the packed bed comprising the composition by means ofadsorption, while the remainder of the unwanted fission products isremoved along with the aqueous solution.

The composition of the invention with the adsorbed Mo-99 is then treatedwith an acid solution (such as sulphuric acid) containing SCN⁻, SO₃ ²⁻and I⁻ ions, as in U.S. Pat. No. 5,508,010, to dissolve the MnO₂ and theadsorbed Mo-99. Again, a complex of [Mo-99(SCN)6]³⁻ is formed. However,whereas the process described in U.S. Pat. No. 5,508,010 requires afurther step of separating out the [Mo-99(SCN)₆]³⁻ complex using acolumn comprising a Chelex resin compound, this step is effectivelycombined with the previous separation step in the process of theinvention. This is because of the compound of formula (I) which isinitially coated with the MnO₂. The presence of this compound enablesthe [Mo-99(SCN)₆]³⁻ to be retained by the composition as it is chelatedby the compound of formula (I) in a similar manner to when the Mo-99 isadded to the Chelex column in the process of U.S. Pat. No. 5,508,010.The use of the composition of the invention in the separation processtherefore removes the need for a separate purification step using aChelex-containing column, since the composition, comprising such achelating agent, can carry out this function instead by selectivelychelating the [Mo-99(SCN)₆]³⁻ complex as it forms. The separation andpurification steps are therefore effectively carried out in anintegrated step. This speeds up the whole separation process, which willincrease the overall yield since less of the Mo-99 will have decayed.The composition of the invention also allows the combination of twoconsecutive process steps, thus minimising the loss of Mo-99 evenfurther to increase the overall yield obtained.

Following this step, the final removal of the Mo-99 from the compositionof the invention can be carried out in a similar manner as in U.S. Pat.No. 5,508,010, e.g. by treatment with caustic soda solution (forexample, a 1M solution), which may be heated to 50° C., although thistemperature is not essential. During this final step, the[Mo-99(SCN)₆]³⁻ complex is broken and the anionic [MoO₄]²⁻ is formed andsubsequently eluted. Any Mn from step (ii) which is not washed away butis bound to the compound of formula I, will be retained on the compoundof formula I following the final step. The separation of Mo from anycontaminating Mn is thus effected. Some of the other metals mentionedherein may form precipitates during the final basifying step. However,these metals may still be eluted from the compound of formula I byrepeated washing with base.

It will be appreciated that this process may be employed for thepurification of other desired polyvalent metal species, by means of theselective formation of anionic complexes in acidic solution, allowingthe chelation thereof by the exposed Chelex. It will further beunderstood that the method and composition of the present inventioncannot be used to separate polyvalent metal species having similarcomplexation behaviour from each other. However, the method andcomposition may readily be used to separate such metal species fromother contaminating components that may be present.

When the composition is in particulate form, the particles of thecomposition may be of any size, but are preferably between about 0.1 mmand 0.5 mm in size. While the particle size of the MnO₂ is an importantfactor to be considered to minimise loss of the smaller particles duringthe process described in U.S. Pat. No. 5,508,010, it is not a majorfactor in the composition or process of the invention. In the invention,the MnO₂ is chemically bound to the compound of formula I (e.g. as acoating on particles of compound of formula I). This avoids the problemof the loss of the smaller MnO₂ particles seen during the washing of theprior art MnO₂ columns. In some embodiments of the invention, however,the particles of the composition, contained in a column for example, arewashed prior to the addition of the fission products to eliminate anysmall and/or loose particles of MnO₂, such as those of about 0.1 mm insize or less, via a process such as liquid sedimentation. This involvesforming a slurry and allowing the sedimentation, where the liquid usedto form the slurry carries the fine particles on or near its surface,this portion of the liquid then being removed.

An alternative means of removing loose particles of MnO₂, or excessivelyfine particles of the composition, is to fill the column with wetsedimented composition such that the column is flooded with water, andthen to blow air through the column from the bottom for a short period.This can be carried out more than once, if desired.

As the MnO₂ coating of the particles is somewhat susceptible to abrasionduring the column elution process, further fine loose particles smallerthan 0.1 mm may be formed which may be removed in the same manner asdescribed above.

In another aspect, the present invention provides an apparatuscomprising a vessel, the vessel having an inlet for the introduction ofa solution containing a desired polyvalent metal species, and an outletfor the elution of components of the solution, the vessel being providedwith a composition of the invention as described above.

The inlet and outlet of the vessel may, in certain embodiments, be thesame part of the vessel, i.e. acting as an inlet when the vessel isbeing charged, then acting as an outlet for discharging of the vessel.In preferred embodiments, however, the inlet and outlet are separateparts of the vessel. In particular embodiments, the vessel is in theform of a column, which may be substantially cylindrical in shape,having an inlet at one end thereof and an outlet at the other endthereof. Such a column may be connected at its inlet to the output ofchemical processing equipment (e.g. processing equipment downstream of aradioisotope (e.g. Mo-99) generation facility (e.g. nuclear reactor orcyclotron), such as a chemical reactor (e.g. dissolver), conditioningvessel or a purification column), and at its outlet to a collectionvessel or to further purification apparatus.

Any of the preferred or optional features of the composition or methoddescribed above may also be applied, as appropriate, to the apparatus ofthe invention.

The present invention will now be described in more detail by way ofexample only.

EXAMPLE 1 Preparation of Resin Composition of the Invention

The composition of the invention may be prepared using conventionaltechniques for producing MnO₂-adsorbates on solid materials. The methodused in this Example is based on an analogous methodology for producingMnO₂ on alumina.

The resin composition was prepared as follows:

-   -   50 g of Chelex 100-200 mesh (available, for example, from        Bio-Rad Laboratories, Inc. (Hercules, Calif.) or Sigma Aldrich)        is placed into a glass beaker and mixed with 50 ml of a solution        of 0.24 M KMnO₄, Stir the slurry thoroughly for about 30 min.    -   Filter the slurry and add the purple coloured Chelex into a        beaker with a solution of 0.64 M MnSO₄ (or MnCl₂) pre-heated to        about 90° C. Stir the slurry thoroughly for about 30 min. In the        case of using MnCl₂, the reaction temperature can be about        20-25° C.    -   The slurry is then filtered and washed with demineralised water        (e.g. 6-10 times).    -   The final material is then placed in an oven at 60-70° C., for        example for about 10-15 hours.        The product resin composition can then be used according to the        invention. It will be appreciated that the above recipe is        designed for producing a small batch of resin composition. The        process can, however, be readily scaled up to produce larger        batches.

EXAMPLE 2 Purification of Mo using a Composition of the Invention

A number of tests were performed with different samples of the resincomposition of the invention, which may be prepared, for example,according to Example 1. These tests tried to simulate the prior artprocess purification step (described above) in which the MnO₂ bed isemployed.

The purification using a composition of the invention is divided intofour steps: loading, washing, pre-conditioning and dissolution. Thepresence (or absence) of Mo in the solution collected after each ofthese steps (except the dissolution step) was verified byinductively-coupled plasma atomic emission spectroscopy (ICP)measurements. The dissolution step was examined by a visual inspectionof the disappearance of the MnO₂ coating layer on the Chelex and also bya visual inspection of the colouring (to a red colour, resulting fromformation of the Mo-thiocyanate complex described above) of the Chelexresin, indicating the adsorption of Mo from the solution.

The same procedure was used for each test, as follows:

-   -   2 g of the resin composition of the invention [samples 1 and 2]        is placed into a glass column. The loading solution is prepared        by dissolving 0.073 g of MoO₃ in 200 ml NaOH (2M). 2 ml of the        resulting solution is acidified with 2 ml HNO₃ (6N). 2 ml of the        resulting solution is loaded into the column and the solution is        collected in a 10 ml vial: Loading Solution (LS)    -   The column is further washed with 10 ml of a solution of KNO₃        (0.1M) in HNO₃ (2M). This solution is collected in a 10 ml vial:        Washing Solution (WS)    -   The column is then conditioned with 3×10 ml 0.05M K₂SO₄. The        second portion of 10 ml is collected in a 10 ml vial:        Conditioning Solution (CS).    -   The dissolution (of the MnO₂ coating) is performed by flushing        the material into a beaker with demineralised water, followed by        the addition of a solution containing: 15 ml H₂SO₄ (9M), 0.2 ml        KI (1M), 20 ml Na₂SO₃ (1M) and 5 ml NH₄SCN (6M), at once into        the slurry. This solution is the Dissolution Solution (DS)

Calibration solutions for the ICP measurements were prepared as follows:250, 500, 750, 1000 and 1250 μL Stock-solution (the concentration ofwhich was 0.1 mg/mL; prepared using Mo-standard solution 1000 μg/mL(BAKER 5769), 10 mL of Mo-standard being made up to 100 mL with 0.1 NHNO₃) were separately pipetted into 100 ml volumetric flasks. These wereadjusted to 100 ml with 0.1N HNO₃. The concentrations of Mo are: 250,500, 750, 100 and 1250 ppb in these solutions. The Mo concentration wasmeasured at 3 wavelengths: 202.032 nm, 203.846 nm and 204.598 nm,simultaneously.

The solutions LS, WS, and CS were subjected to ICP analysis. In the caseof LS, the sample was treated prior to analysis by filtration, thendilution 1:1 with 0.1M HNO₃.

The results of the ICP analysis and visual examination of the solutionsLS, WS, CS and DS are presented in Table 1.

TABLE 1 ICP analysis and visual inspection of test solutions ResinProcedure step Sample LS WS CS DS 1 absence of absence of absence of AllMnO₂ dissolved Mo Mo Mo Chelex red-coloured at all at all at allwavelengths wavelengths wavelengths 2 absence of absence of absence ofAll MnO₂ dissolved Mo Mo Mo Chelex red-coloured at all at all at allwavelengths wavelengths wavelengthsThese test results illustrate the feasibility of using a resincomposition of the present invention to purify suitable metals (Mo inthis Example) in a ‘one-pot, one-shot’ manner. In particular, it isshown that the Mo is retained on the MnO₂-coated resin, but thentransferred to and retained by the Chelex when the MnO₂ coating isremoved. The removal of the need to conduct two separate purificationsteps (as in the prior art) should make the purification more efficientand therefore provide the potential for a higher yield of the desiredmetal species.

1. An apparatus for separating a polyvalent metal species from one ormore accompanying impurities comprising at least one vessel, the vesselhaving an inlet for the introduction of a solution containing thepolyvalent metal species, and an outlet for the elution of components ofthe solution, the vessel being provided with a composition comprising:MnO₂ and a compound of formula (I)

wherein: R is a polymer; each Y is independently a hydrogen or anegative charge; Z is either hydrogen or is not present; each n isindependently 1, 2, 3, 4, 5 or 6; and wherein at least 50% of thesurface of the compound of Formula (I) is coated with MnO₂.
 2. Theapparatus of claim 1, wherein the vessel is in the form of a columnhaving an inlet at one end thereof and an outlet at the other endthereof.
 3. The apparatus of claim 1, wherein the apparatus comprisestwo vessels, first and a second column, wherein the first column isconnected to the second column such that the eluate from the columnenters the second column.
 4. A method for separating a polyvalent metalspecies from one or more accompanying impurities, comprising: (i)contacting the polyvalent metal species and accompanying impurities witha composition comprising MnO₂ and a compound of formula (I):

wherein: R is a polymer; each Y is independently a hydrogen or anegative charge; Z is either hydrogen or is not present; each n isindependently 1, 2, 3, 4, 5 or 6; and wherein at least 50% of thesurface of the compound of Formula (I) is coated with MnO₂ such that thepolyvalent metal binds to MnO₂; (ii) dissolving the MnO₂ bound to thepolyvalent metal to form a solution; and (iii) contacting the solutionwith a complexing agent, such that the polyvalent metal binds to thecompound of formula (I).
 5. The method of claim 4, wherein the methodfurther comprises releasing the polyvalent metal species with a base. 6.The method of claim 4, wherein the dissolution of step (ii) isfacilitated with an acid.
 7. The method of claim 6, wherein the acid issulphuric acid.
 8. The method of claim 4, wherein the polyvalent metalspecies is selected from the group consisting of Mn, Co, Ni, Pt, Mo, andFe.
 9. The method of claim 4, wherein the polyvalent metal species isMo.
 10. The method of claim 4 wherein the polyvalent metal species is aradioactive isotope.
 11. The method of claim 10, wherein the polyvalentmetal species is Mo-99.
 12. The method of claim 4, wherein thecomplexing agent in step (iii) comprises rhodanide ions.
 13. The methodof claim 4, wherein step (iii) additionally comprises a reducing agentselected from the group consisting of iodide ions, sulphite ions,metallic zinc, metallic aluminum, and combinations thereof.
 14. Themethod of claim 4, wherein the composition comprising MnO₂ and acompound of formula (I) is provided in one or more vessels having aninlet for the introduction of a solution containing the polyvalent metalspecies, and an outlet for the elution of components of the solution.15. A method for separating Mo-99 from one or more accompanyingimpurities, comprising: (i) contacting the Mo-99 and the accompanyingimpurities with a composition comprising MnO₂ and compound of formula(I)

wherein: R is a polymer; each Y is independently a hydrogen or anegative charge; Z is either hydrogen or is not present; each n isindependently 1, 2, 3, 4, 5 or 6; wherein at least 50% of the surface ofthe compounds of Formula (I) is coated with MnO₂, such that Mo-99 bindsto MnO₂ and (ii) dissolving the MnO₂ bound to the Mo-99 with an acid toform a solution; (iii) contacting the solution with a rhodanidecomplexing agent such that the Mo-99 binds to the compound of formula(I); and (iv) releasing the Mo-99 bound to the compound of formula (I)with a base.
 16. The method of claim 15, wherein the compositioncomprising MnO₂ and a compound of formula (I) is provided in a vesselhaving an inlet for the introduction of a solution containing thepolyvalent metal species, and an outlet for the elution of components ofthe solution.
 17. The method of claim 15, wherein R comprises acrosslinked polystyrene and n=1
 18. A method for producing aMnO₂-adsorbate, wherein the method comprises contacting a manganesesalt; and a compound represented by the general formula (I)

wherein: R is a polymer; each Y is independently a hydrogen or anegative charge; Z is either hydrogen or is not present; each n isindependently 1, 2, 3, 4, 5 or 6; and wherein Formula (I) is coated withMnO₂.
 19. The method of claim 18, wherein R comprises a crosslinkedpolystyrene and n=1.
 20. The method of claim 18, wherein the compound offormula (I) of the MnO₂-adsorbate is coated with MnO₂ on at least 50% ofits surface.
 21. The method of claim 18, wherein at least 90% of thesurface of the compounds of Formula (I) is coated with MnO₂.
 22. Themethod of claim 18, wherein the method further comprises heating theMnO₂-adsorbate at a temperature of 60-70° C.
 23. The method of claim 22,wherein the heating is conducted over 10 to 15 hours.